The present invention relates to plasticizers for polyvinyl chloride and compositions thereof.
Since polyvinyl chloride (PVC) is a relatively brittle material at normal temperatures, so-called plasticizers are added to it for use in numerous fields of application. Plasticizers are, in general, high-boiling organic liquids which are able to form a homogeneous solid phase with polyvinyl chloride.
However, a good plasticizer should, in addition to its plasticizing action, also exhibit the following properties when used with polyvinyl chloride:
(1) High gelling capacity; this means that a polyvinyl chloride/plasticizer mixture should gel as rapidly as possible and, hence, should be ready for further conversion processing within a short time. PA0 (2) Low volatility; that is, high migration resistance. PA0 (3) High strength and surface hardness. PA0 (4) Good dielectric behavior.
Numerous esters of phthalic acid are already known as plasticizers for polyvinyl chloride. The most estensively used plasticizers include butyl benzyl phthalate, dinonyl phthalates, di(cyclohexyl) phthalate, di-(methyl-cyclohexyl) phthalate and di-(2-ethyhexyl) phthalate (dioctyl phthalate). Butyl benzyl phthalate exhibits several disadvantages: it has an intrinsic odor, is comparatively volatile, and is not light-resistant (compare Ullmanns Enzyklopadie d. techn. Chemie (Ullmann's Encyclopaedia of Industrial Chemistry), volume 18, (1967), page 560). The nonyl phthalates above all exhibit a relatively unsatisfactory gelling capacity. Di-(cyclohexyl) phthalate is a powder which melts at about 64.degree. C. and di(methylcyclohexyl) phthalate has an unacceptably high viscosity of 15,000 to 25,000 mPas at 20.degree. C. Hence, their usefulness as plasticizers is limited.
Because of the problems described, compromises must often be struck when plasticizing polyvinyl chloride. For example, mixtures of plasticizers are employed. In doing so, those plasticizers are selected which bring about a particular desired property and in spite of being mixed with other plasticizers impart this property to the finished plastic. However, it would be desirable to have substances which do not require such compromises and can be employed as sole plasticizers. Di-(2-ethylhexyl) phthalate does exhibit satisfactory values of the important properties of gelling capacity and migration resistance; but these values undoubtedly still warrant improvement.